Electron-Magnon Interaction in Ferromagnetic Semiconductors

Abstract

The interaction between conduction electrons and localized moments in degenerate ferromagnetic semiconductors has been studied, assuming Bloch states for the conduction electrons and using the low-temperature spin-wave approximation. The finite-temperature Green's-function formalism has been used to obtain the real and imaginary parts of the electron and magnon self-energies, from which the electron and magnon energies, lifetimes, and specific heats have been calculated. It is found that the conduction-electron energy corrections as a function of electron wave vector behave quite differently for the two conduction-electron spin polarizations, and hence the effective masses and mobilities of up-moment conduction electrons are quite different from those of down-moment electrons. The electron lifetime associated with magnon scattering is short enough to make this a dominant contribution to the electron lifetime in magnetic semiconductors. The electronic specific heat in magnetic semiconductors is small owing to the small number of conduction electrons, and the correction to this specific heat arising from the electron-magnon interaction is also small. The magnon specific heat, on the other hand, is quite large in magnetic semiconductors at low temperatures, and as a result of the change in the magnon spectrum due to the electron-magnon interaction, there is a substantial correction to the magnon specific heat. All of these effects are quite strongly dependent on carrier concentration. Thus, by varying the doping it is possible to see dramatic changes in these effects.